We plan to study the regulation of enzymes requiring vitamin B6 and folic acid, involved in the metabolism of serine and threonine. Special emphasis will be placed on the relationship of these reactions to homocystinuria neogenesis of labile methyl groups, metabolic pathways and control mechanisms in mammalian systems. The enzymes: serine-theorine dehydratase, serine hydroxymethylase threonine aldolase, and methylene tetrahydrofolate reductase.